I have no experience with Rieco jacks only Atwood and Happi Jack, but I've repaired a few RVs.
I use the Dicor self-leveling sealer on both the sides and roof and on EPDM, Aluminum, and Fiberglass. I'm not familiar with the SixPac roof, is it EPDM? I tried the regular Dicor a time or 2 but with the self-leveling I've always gotten a nicer looking job. I have tried Geocel products which cure more like silicone. They may be as good as Dicor but I found them harder to make them smooth out and look good and they don't dissolve as easily with mineral spirits.
The silicone is sometimes a pain to remove but you will be please with the result once it is gone and the job is done. I've found that mineral spirits will remove standard caulking and sealers (except silicone) without damaging the paint as long as you don't have to scrub too hard. It will sometimes cause silicone to start to loosen (especially if it is very thin) but you will still need to scrape.
I have used (very very carefully) acetone on EPDM to remove tuff deposits. If you use too much it will cause the EPDM to expand, causing what I call a pucker in the material. Mineral spirits can also expand EPDM roofing if too much is applied, and what "too much" is will vary on the composition of the EPDM. It can take a day or 2 for the rubber to relax again. The very careful part is that acetone will melt plastic and will remove paint very quickly. It is outstanding for cleaning fiberglass.
To keep from damaging the siding or roofing, I use a plastic putty knife. They will dull after a bit of uses but you can touch them to a sanding belt at the right angle and create a new edge. Additionally, they are only 79 - 99 cent.
As for the bottom, I have used Flex Seal to repair small areas. It's kind of like a tar plastic mix. It doesn't stay soft like some undercoating. Someone at Arctic Fox recommended that I use Rustoleum truck bed liner. He said that this is the material used on there units and it can be bought reasonably and locally just about everywhere. I'm about to do that on my current home project.
When you need info ask. Someone on RV.net has probably been there and can help. Most of the info is opinion, so weigh the common sense of the answer. And, don't get upset with the nay sayer's, narsicists, and those that like to argue, they have nothing better to do. They're all opinions and most really like to help.
Good luck.