A logical argument, but I doubt there will be a long-term effect. Current fuel prices are as high (even after adjusting for inflation) as they have ever been, and full-size trucks and SUVs sell very well. In the RV area, very large motorhomes (including those bus-derived coaches) seem more common than ever.
I recall reading that during previous "gas crises", industry observers have noted that other than very short-term fluctuations (sales "stalling out for while"), only a shortage of
supply - not prices - affects luxury vehicles, including RVs. If you can afford a $200,000 RV, you can buy the fuel for it. If you have a full-size truck, you're probably not going to pull a smaller trailer than you like just to save fuel. You might use it less... but even that's uncertain.
We have a
Boler 1700 because it fit our needs as well as any trailer we could find that was within our tow vehicle's capacity, and we didn't want to drive a larger vehicle. If fuel were cheaper, we'd still have the
Boler; if it doubles in price, we probably won't trade down in size.
With fuel being a minor part of vehicle operating expenses (after depreciation and insurance, and comparable to maintenance), the price of fuel isn't a very effective driver for vehicle choice. Honda once offered the Civic in several versions, including one (the VX) which was not the cheapest but did get the best fuel economy, at the expense of performance and ride comfort; they could barely sell them, and gave up after a short period. People say they care about fuel consumption, but it's not really important to most of them.