Thanks for the follow-up information.
The 198RD as you mentioned has a published UVW of 3,830lbs, but the actual ship weight from the factory will be around 4,030lbs (GVWR of 5,900lbs). If there is a 198RD on your RV dealer's lot, look for a yellow sticker for the actual factory UVW, that's your starting point. Then add another 75lbs for RV dealer battery, misc., etc..
So (4,105lbs) + (500lbs conservative cargo estimate) = 4,605lbs TT weight.
Your Tacoma's Tow Rating of 5,000lbs is based on it's curb weight, not as it sits in your driveway..., so any option weight (cap, upgrades, etc.), passenger weight, and cargo weight in the Tacoma gets subtracted from the 5,000lb tow rating.
Tow Ratings: http://www.jaycoowners.com/forums/f37/what-is-my-actual-tow-rating-3866.html
With your Tacoma's "actual" tow rating dropping below 5,000lbs and the 198RD's loaded weight actually approaching 5,000lbs (possibly exceeding), IMO you will be maxing out your Tacoma's weight limits at the very least...., and that's under some very controlled loading habits.
Hope this helps.