Some more information will help to determine how good or bad this will be. You have 2 different tow vehicles that have different suspension systems. The Highlander is a SUV. The Frontier is a small pick up truck, they will react different to the same loaded tongue weight of a trailer.
Your normal TV, which I believe is the 2016 Toyota Highlander, how was the WD hitch setup to tow the trailer? Did the dealer do this for you when you bought the camper? If so, odds are high the trailer was not loaded with camping gear. Once you load the camping gear the WD hitch may need to be readjusted to compensate for proper WD on the truck for the added "loaded" trailer tongue weight. Has this been done yet?
When towing with the Highlander, is the TT, level, nose low or nose high and by how much? This would help to know where you are starting from.
The Frontier, I do not know, is this the crew cab or a standard cab? Not that it matters that much, but it would help in estimating the difference between the 2 trucks. The suspension of the pickup truck is different then the SUV.
You said this,
Kirk wrote:
I measured the distance from the ground to the bottom of the hitch receiver, and the Frontier sits one inch higher than the Highlander.
You really cannot tell by just measuring the hitch receiver how the WD on the truck will be affected. Just because unhitched it is 1 inch higher does not mean when the camper is loaded up and hitched it will come out 1 inch higher.
Have you hooked up the camper to the pickup and if so how level was the trailer? Level, nose down or nose up and by how much?
You may very well be able to switch between trucks with very little changes in the hitch setup, but from your note, we have no idea how your SUV is setup and if the camper is loaded or not. The PU has a truck bed and it may carry more cargo then the SUV.
I would say this, load the camper and the SUV that you tow with normally and optimize the WD on the truck and get the trailer to tow as close to level as practical.
Then take that hitch head settings that optimized the SUV and go load the PU truck with all the gear it would have in the truck bed to go camping and see how that setup comes out. You may find the PU with extra gear in the truck bed changes the setup enough to not worry about it or to think through maybe a setting change may be needed.
Bottom line: We and you really cannot tell if a towing setup is acceptable by just measuring an unhitched receiver height on 2 different vehicles.
Hope this helps
John
2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10 RA, 21,000 GCWR, 11,000 GVWR, upgraded 2 1/2" Towbeast Receiver. Hitched with a 1,700# Reese HP WD, HP Dual Cam to a 2004 Sunline Solaris T310R travel trailer.