Hi Charles,
I think everyone on this forum understands your confusion from first hand experience they've had at some point. I find that most dealers don't really know or care about the limits etc - they're in it for the sale and its buyer beware.
You're right, A Toyota Tundra is not a good truck for the Lance 825 camper. It all boils down to the truck's GVWR versus all of the cargo in the truck, including the truck's wet weight, passengers, food, camper, water in the camper etc etc etc.
I personaly find the camper manufacturer's are a little mis-leading with regards to what truck will carry thier camper but they always mention the phrase "do not exceed your vehicle's GVWR" which is their CYA.
If you exceed your truck's GVWR and you get in an accident, you just gave your insurance company a legal out. They don't have to cover you since you exceeded your truck's capabilities. You could also be looking at a fine for driving an over-loaded vehicle. With this said, I'm pretty sure most people violate the GVWR by a little (or maybe even a lot). You can add airbags to make the ride better but even the airbag manufacturer states "do not exceed your vehicles GVWR". You'll see this phrase all over the place, everyone is out to cover their butts.
When you calculate the numbers, make sure you include passengers, luggage, food, fresh water in the camper tanks (8.5lbs/gal), turnbuckles, tie downs, any acceesories added to the truck, any accessories add to the camper, fuel in the truck's tanks (8lbs/gal), propane (40lbs)... the list goes on and on and it adds up in a hurry.
When I bought my rig, I bought the truck first and the camper second. I figured I'd get the biggest truck I could and got a Dodge 3500 Dually with a GVWR of 12200lbs. I figured I could carry any camper then, without worry..... Ha!
I then built a spreadsheet comparing the weights of a bunch of campers with accessories and added in the turnbuckles, hitch, tiedowns, water in the tanks etc. Most that I was looking at put me over my truck's GVWR. When it came down to it, the camper I did buy (which weighs just under 3000lbs wet) plus all the other stuff, family included, came in at 72lbs under my truck's GVWR limit. When I hook up my trailer I have to make sure the water tanks in the camper are empty or I'm over the limit. I went to my local weigh scales and measured it all fully loaded so the numbers are accurate. In hind sight i would say selecting the camper first is the better way to go but do the math of both the camper and truck to make sure it all fits before you buy anything.
In the end, (and sorry for the long winded response) to be legal on the road, don't exceed the truck's GVWR. Oh, and there's no easy answer to the question "will this camper fit this truck?"
A WORD OF CAUTION for readers of this post. Ignore the suggestions that your insurance won't cover you in an accident if you exceed your GVWR. READ AND UNDERSTAND YOUR INSURANCE POLICY. IF YOU DON'T UNDERSTAND THE POLICY, CONTACT YOUR AGENT OR THE UNDERWRITER FOR CLARIFICATION.
Exceeding your vehicle GVWR may very well void your new vehicle warranty, but most insurance policies do not and cannot exclude coverage for this reason.
This reader has encountered a lot of misinformation on these sites. VERIFY, VERIFY, VERIFY.