[slowmover]

That Shasta isn't the one on Pirate4x4 is it? (Any and all tech articles on WOODALLS by JBarca are best on net. Leaf spring maintenance, upgrades, brakes, etc. Also his on using Reese Dual Cam Straitline Hitch. See also LAdams and others. Let me state emphatically that shock absorbers, increased wheel travel and crossmembers are part of what make my high end trailer so much nicer to tow. Greater safety. And higher FE).

Best RV tech online I know of is "Lewster" on Airforums. Between being factory authorized service and his million dollar motorhome customers he's always a good read on what and why. A pair of Lifeline GPL-6CT will be an upgrade on my Silver Streak. I may may even hang an extra on the truck frame. LiOn just too expensive for me. His lengthy comments in many posts on many threads at that forum worth reading. In fact, I'd use his recommendation on any RV system as default prior to further investigation.

Love the topper! Similar in shape to an all aluminum topper DIY this site on a Dodge Diesel like mine. Bob reports its worth between 1-2 mpg on the ANNUAL average MPG.

And allow me a suggestion for A-B testing. Choose an easy highway roundtrip for comparison sake. Fill up before and after trip. Use cruise control set at 60-mph. Even if weather different with completed topper (even loaded versus unloaded), it'll be a useful reference solo and towing. I'd do this ASAP on the solo, stock run.

I also recommend weighing the truck on a CAT Scale. Any all configurations. Gas motors are highly weight sensitive. Best to be able to factor that out. The more numbers you accumulate, the easier it will be to extrapolate what, if any, savings are present and where future gains may be had.

Same for setting WD hitch with trailer. Scale numbers necessary to suss out best performance. Best handling, braking and FE go hand in hand. (More in my posts on other threads). Same speed solo and towing for testing purposes means more than weather vagaries (barring high winds or xtra cold temps)

FWIW, the usual MPG drop from solo to towing (all other factors the same) is 40%. Having a strong number for solo MPG (and weight) is a foundation for all further testing. And, setting hitch.

I'm of the opinion that treating each of the vehicles aero separately in a combined rig is the best approach. Get those numbers, and future mods will be more realistic.