It'll be interesting to hear what the specs have to say (GVWR, GAWR, GCWR, etc.). I'd guess the V-8 is the 5.4 Triton which is what I have in my tow vehicle (3/4 ton camper van). I've looked at a number of 21' or so RV's, and they had good towing specs; but they also all had the V-10 version of the same engine (and perhaps a different transmission).
You probably know this already, but I'll mention it just in case. There may or may not be an actual "tow rating" for this particular RV. And even if it has one you still may not "be able" to pay attention to it (because of other factors). It's sort of like a ground tackle system in that you have to look for the weakest link and then that's the limit. For example, my van cannot tow up to it's actual tow rating, because I hit something else first (in my case, the GCWR). I still have plenty of capacity for towing the C-Dory 22, however. (The math shows that I have around 5,500# available to me for towing out of a theoretical 7,500# tow rating -- however I hit the GCWR at that 5,500# figure due to the fact that the van is not empty but instead has camper outfitting in it. The other ratings all have "room" left in them.)
So, if there is no rating, or even if there is one, what I would do is look at all of the following, and see if/where the "real world" limit is. One of these will probably hit the limit before the others:
1) GCWR
2) GAWR (rear)
3) Tow rating (if there is one)
4) Hitch rating (if this is the first "weak link" but there is room in all the other figures, it can possibly be raised by changing to a better hitch).
5) Tongue weight limit.
If you are going by calculations (prior to purchasing, for example), note that if there is a long overhang (distance between rear axle and hitch) that the weight on the hitch will "become more weight" on the rear axle. This can be calculated if necessary. Of course if you already have the vehicle you can weigh things.
There is also the GVWR, which as Bob mentioned is sometimes fairly close to being maxed out on RV's (before towing). Not always though.
Sunbeam