So long as you can get from the original builder a build log showing they built (or if the kit changed hands several times, for each successive builder) the majority - 51% - of the kit, it will be eligible for an Experimental - Amateur Built CoA. You just can't sign off on the MR is all, so will have to pay a LAME to do it, or if you are keeping it local, you might be able to persuade the original builder who does have the authority to do it for you while you follow through. If you go RAAus, it is a moot point anyway as a L1 (RPC holder) can sign off on it, so long as it is not used for hire/reward.
Truth be told, RV's and their ilk are so basic, the LAME costs for the annual would take years to get back in terms of "build it yourself" savings. 1000 hrs build time at $30/hr is not unreasonable, and that is a *lot* of LAME time! Plus, you would get to fly right now, rather than build for several years. And now your $100,000 RV has effectively cost you $130,000 as opposed to buying someone's already-flying RV and having the LAME do the inspections for you.
What sort of RV are you considering, anyway?