When we were shopping, we looked at a Coleman with a similar layout to the 198RD and really liked how light and bright the back of the trailer was with the dinette and sofa.
As long as you're not loading up the F150 with cargo, I'm willing to bet you're within specs on size.
You also should look up the engine details on what RPM is max horsepower and get comfortable with the idea you might need to run at or near that range when climbing hills. Some people get freaked out at the idea of running for any time above 2,500 RPM.
I've done multi-mile stretches in 3rd gear in my SUV and the temperature gauge never budged over where it sits while I'm driving around town without the TT.