Welcome to the forum
Fuel savings. Depends on what kind of mileage your going to get and the cost per liter. I can say from years of experience that towing any large fifth wheel, a diesel truck is the way to go.
We don’t sell Keystone trailers at my dealership, but we do sell Grand Design. The reflection is a very nice unit, and built well. They PDI with few issues so take it for what it’s worth. GD is now owned by Winnebago and I can’t say I’ve seen any significant drop in quality.
Good luck in your decision, and even if you do buy the reflection, your welcome here.
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.