Continuity mistake: When the Munros pick up Gretchen at her house, many shadows are cast on the lawn. Later, when they drop her off, the shadows are identical - they have not changed a bit. (00:03:20 - 00:05:25)
Continuity mistake: After being snubbed by Carl and Cassie, when Bob walks into the kitchen as Jamie speaks to her sister, the chopper jumps to the other side of the butcher block cutting board, and the chair beside the laptop turns by itself, etc. in following shots. (00:06:30)
Continuity mistake: When Bob speaks to his coworkers at his office, Bob says, "Bring jewelry," and his glass is nearly empty, but a couple of shots later, as he still sips his straw, the glass actually has more liquid now. (Difference only visible on fullscreen DVD.) (00:08:45)
Continuity mistake: After Bob comes home with the RV, when he and Jamie walk into the kitchen there is a butcher block cutting board laden with items, at the edge of the counter. However, when they speak beside that island counter the cutting board is gone. (Even more noticeable on fullscreen DVD.) (00:10:20)
Continuity mistake: In the RV, Jamie puts stacks of dishes away in the overhead cabinet - second from right, when Cassie moves Carl off the couch. When Bob makes the sharp right turn, the dishes pour out of the overhead cabinets, but the ones that come out of the second cabinet are not the same dishes that Jamie put away. (00:12:20 - 00:15:00)
Revealing mistake: When Bob has difficulty with his seat belt at the start of the road trip, the side-view mirrors have a translucent finish, just as in other shots throughout the film; however, the mirrors' surfaces are normal in the rest of the shots. Deliberately done to obscure the reflection of the crew. (00:13:20)
Factual error: When the family is beginning their trip, Bob has difficulty putting the RV in gear. We hear gears grinding despite the fact that the vehicle obviously has an automatic transmission (as evidenced by the column shifter). Automatic transmissions do not contain the same type of gearbox as manual transmissions, and it is impossible for an automatic to create a gear-grinding noise. (00:13:30)
Continuity mistake: At the start of the road trip, when Bob tries to maneuver and turn the RV around on their street, the interior shots looking out and the exterior shots do not match up in consecutive shots, regarding the homes and gardens, etc that are seen. (00:13:45)
Revealing mistake: When the Munros begin their trip, as Bob makes the sharp right turn the RV's pop-out begins to open directly behind him, and its left wall is missing - we can actually see the RV's window at the opposite side, through the opening. (00:15:25)
Continuity mistake: In the RV, when Bob turns around to glance at Cassie after the dishes fall on her, in the first shot his arm rest is up (look beside his right shoulder) as he faces her, but when he says, "My bad," the arm rest is down. (00:15:30)
Continuity mistake: After the Big Rolling Turd runs over the grocery carts, Bob's shirt goes from having four buttons buttoned up, then to five, back to four, then back to five again. (00:16:20)
Continuity mistake: After the Big Rolling Turd has rolled backwards over the grocery carts, in the shot of the RV heading down the highway the back center window curtain is hardly open. In the following interior shots, as they sing, the entire curtain is open, but in the last exterior shot it is hardly open again. (00:17:15)
Visible crew/equipment: When everyone is singing their own song (except Robin Williams), the last shot of this scene shows the back of the RV. As the camera pans down, you can see several cars reflected in the window, one of which is the crew's truck with the camera crane erected above it. (00:18:35)
Revealing mistake: The Munro's RV has a large pop-out (slide-out) on its left side, behind the driver. When the pop-out is closed one side wall should be directly behind the driver's seat, but that wall is gone - it has been deliberately removed. As a side note, when the Munros rush to leave before Mary Jo Gornicke reaches them, that wall (with a small window) is seen in the exterior shot, as it slides in. (00:19:15 - 00:39:30)
Continuity mistake: After Travis hoses the turd off Bob, when Billy remarks that 'Ernest Goes to Jail' is funny, the boy's left front tooth (viewer's right) is fully grown in; however, that evening, after dinner, Billy's tooth is barely halfway grown in. (00:28:55 - 00:37:00)
Continuity mistake: When the thoughtful gentleman offers Cassie the 'vegetarian' organ stew things on the table disappear, reappear and change between shots, such as Earl's plate, the flowers, etc. (More visible on fullscreen DVD.) (00:32:50)
Continuity mistake: When the Gornickes get ready to sing for the Munros, Earl gives Billy the red kazoo, which is seen in the front shots, but in the side shots Billy holds nothing. (00:33:55)
Continuity mistake: After Jamie pinches Carl's ear because he spills their destination, when Mary Jo walks toward the Munros, Billy's back faces the camera as he stands on the ground, away from the bus. However, in the next shot Billy faces the camera as he stands on the stool while leaning on the bus. (00:35:10)
Continuity mistake: When Mary Jo begins walking to the RV at 6:00 AM, Bob and Carl remove the tire blocks outside, while Jamie closes the "stupid pop-out thing" inside. In the exterior shot, as it slides in, Bob is sitting with his hand on the steering wheel - though it isn't until two shots later that Bob actually gets back to the driver's seat. (00:39:25)
Continuity mistake: When the RV speeds along at 12 MPH behind the tractor, the shadows keep changing. In the interior shot the shadows are cast to the right of the tractor, but in the exterior shot, as the RV passes, the long shadows are cast to the left of the tractor. (00:40:30)
Answer: In the world of "make believe", they used "movie magic" to zap the RV out of the water and on to dry land - with no mechanical issues resulting from being submerged. In the real world, someone called a tow truck - perhaps AAA - and the RV was pulled out of the water and it suffered water damage and needed some repairs. This movie was presented as being "real life." Bob left on a bicycle to "try to find help." Near the end of the movie, Carl said that the RV "spent two days under water and they had to fish it out." He didn't say who "they" were. A fishing pole would not be strong enough to reel in a large RV, so I think it is safe to conclude that a tow truck was used to pull the RV out of the lake.
KeyZOid
It should be noted that "fish it out" is a common phrase to mean pull or take out, especially after searching. When people use the term, they're never taking about using a fishing pole. But often when people post questions like this, they're asking for an in-film explanation in case they missed (or didn't understand) something. If no in-film explanation was given, a reasonable speculation can be given. You don't need to remind people the movie is a movie. If the in/film explanation is uncharacteristic to real life, then one can point out that in real life it wouldn't happen that way.
Bishop73
It was meant to be ironic.
KeyZOid
There was no irony, but this isn't the forum for irony anyways.
Bishop73
I guess I failed miserably... but wasn't the original question rhetorical?
KeyZOid