Deep Space Lighting — Dave runs Deep Space Lighting, which started out providing headlight upgrade kits for Volvo RV haulers. If you want to do lighting right (as in high-performance and legal), Dave’s the guy. Feel free to ask him your general RV lighting related questions.
RVheadlights.org — Most motorhomes use headlights designed for other vehicles. This site is a resource for locating replacement headlights, upgrades, etc.
Escapees HDT Forum — easily the best resource for heavy-duty trucks being used recreationally. Great community; go here for information on the 3 annual HDT get-togethers. For more general RVing stuff in a more close-knit community than either of the big guys, the Escapees forums are a very good resource.
Heavy Duty Truck Campground Directory — Have a big rig and you’re looking for places to stay? This directory is full of user-submitted locations that are friendly to, and accommodating of, big RV combinations. You’ll find notes about tight turns, access roads, site lengths, etc. If a campground you’ve stayed at fits the bill, there’s a short form to have it added to the directory.
Heavy Duty Truck Resource Guide — Here’s lot of information for using a heavy duty truck as an RV hauler, and lots of articles and documents for various projects of interest to that crowd.
TruckConversion.net Forums — Truck conversion-specific forum. Great resource, but doesn’t get a lot of traffic. If you post a question, be patient.
East Coast HDT Rally — Annual gathering of HDT and truck conversion owners in April in Crossville, Tennessee.
National HDT Rally — October gathering of HDTs and truck conversions in Hutchinson, Kansas.
Passport America — One of the only discount clubs I pay money to belong to–I finally joined in 2017, and wish I’d done it sooner! 50% discounts for short stays at many campgrounds, and the annual fee is cheap enough that it only takes a couple of days to pay for itself.