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)
Revealing mistake: When Bob is on the bus' roof there are interior shots of the bus and all its right side (viewer's left) sliding metal framed windows are visible and intact. After Travis stops short, in the following exterior shots four of the double sliding windows have been deliberately removed from their tracks, so the camera's view of the kids is unobstructed. (01:23:10)
Revealing mistake: After the RV rolls over Bob, in the overhead shot as he lies on the ground, there are two tire tracks - one to Bob's left and another to his right. Problem is that the RV has four rear tires, which actually should have left the imprint of four tire tracks. (01:12:40)
Revealing mistake: When Bob hangs upside down on the Gornicke windshield, in the shot facing the bus as he begins to fall, we can see the driver's and front passenger's seats and Travis, his wife, and Jamie are all gone. Of course they are back in the following shot. (Only visible on fullscreen DVD.) (01:23:15)
Revealing mistake: When Bob throws pitches to Carl while he barbecues, the close-up of the grill shows Bob's arm holding the tongs as he fiddles with the food. Problem is, it is not Robin William's notoriously hairy arm and hand in the close-up. Things on the grill differ between shots as well. (01:01:10)
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)
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)
Revealing mistake: When the RV teeters on the mountaintop, Bob opens the RV door and then swings out, but the three automatic stairs below the doorway do not engage - deliberately done for the humor. (01:10:00)
Revealing mistake: When Bob is riding the pushbike down the steep hill to get to his family and the Gornickes at the bottom, in some shots you can blatantly tell that a stunt double that looks nothing like Robin Williams is riding the bike. The stuntman is also visible later when Bob is on the roof of the Gornickes' bus.
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