Man, I just typed a bunch of stuff and then realized you have a slide in camper.... Haa haa..

You'll probably want to get a 350 for the increased GVWR. I don't know about CA laws and GVWR registration but some states require that you insure a vehicle >10k GVWR as a commercial vehicle, which is pretty hefty from what I've read. If that's the case in CA, get the 250. Either gear set would be fine more than likely, but the 4.30's will give you a bump in oomph but slightly less mpg's. I don't know how the 250's ride, but for a 1 ton truck, mine rides nice (even better now with the 9000's on it). I rarely tow, truck is a daily driver (26 mile roundtrip to work everyday). So my final answer, 350 w/ 4.30's.

Regardless of what you go with, I'd recommend some air bags for the rear. The camper pkg will give you stiffer front springs and a rear anti-sway bar, but unloaded may be a harsher ride. I can't speak to that though, don't have it on my truck. You could always add the rear sway bar after the fact and retain a decent unloaded ride.

Here's the details of the camper pkg:

CAMPER PACKAGE (471)
Availability:
• Optional on all Pickups
Not available with:
• 20" Wheels and Tires, Pickup Box Delete (66D), 3.31 Axle Ratio
(on 4x4 with 17" or 18" tires) or Heavy Service Front Suspension
Package (67H)

Includes:
• Extra heavy-service front springs (4x2) (2 up upgrade above the
spring computer selected as a consequence of options chosen. Not
incl. if maximum springs have been computer selected as standard
equipment)
• Heavy service front springs (4x4) (1 up upgrade above the spring
computer selected as a consequence of options chosen. Not incl. if
maximum springs have been computer selected as standard
equipment)
• Rear stabilizer bar (SRW only)
• Slide-in camper certification
• Rear auxiliary springs (F-250 only)