Trailer Length

Were you looking at a park model or a TT, makes a difference?

Maybe the salesman said that because he was thinking about the refueling of a longer trailer, fitting into tight stations. ( @ 58-60 ft long combo)
I towed a 37 ft with a 250 , all was fine but I had a large fuel tank and picked my fuel stops.
Being you already tow a 35' the extra 3 ' will not matter much as long as you park it to fit in your storage area and don't change your rving style and con't to use large back-in sites or pull thru's.

Tow Vehicle is Chevy Silverado 2500

If you go back a few years any travel trailer 38 feet or longer was basically concidered a park trailer but today more are found on the road. Good luck.

You'll be fine! So when you take delivery of the new camper, spend about 15-20 minutes in the RV dealership's parking lot making a few turns and watching how the trailer tracks behind the tow vehicle. And the practice backing up a time or two.... just to get a good "feel" for the camper and you'll know it's limitations before hitting the road. It's 15 minutes well spent!

(I love bigger campers! It's sooooo nice not to be cramped-up! When we get older, we deserve to spoil ourselves a little!)

Not just the length to consider, but where the length is. So the distance between the hitch and the axles increases a 1' or so, and the distance after the axles increase 2' or so. The impact on maneuverability when you're already used to 35' will be marginal, IMO. The bigger question is will the overall length still fit in the spaces you like and will your tv be up to handling the extra weight. I've set my 35' trailer's tongue down in many "thirty foot" spaces, and we do mainly state parks. I don't see an issue if your numbers fit. I'd go up 3' if my tv was up to it without much thought at all. That's just me.

You didn't mention what you are towing it with. That makes a big difference.

You may be in a market for which seasonal use of permanent sites could be the normal use of larger travel trailers. Another three feet doesn't make that much difference, except when visiting older public parks where many sites are smaller. At 35 feet, you were already in the "too big" category for small campsites.

Thanks for reassurance.....I thought I was missing something.

Once again, a salesman that doesn't have experience in towing creates fear and doubt. Yes! You are fine. Many, many, towables much longer and taken on the road daily. Think about it - not only TT's, but FW's, and even motorized units are much longer. If you are fine with it, then it's good, as long as your TV and unit are setup to handle any possible sway.