They aren't cheap, but I put an Odyssey in my 4 wheeler about 6 years ago. Never charged it and it ill fire right up. I like the AGM batteries as you can mount them anyway you want and they live a long time. When/if I put electric start in my Avid, it will get one for it.. I may get one to replace that led acid battery I have for my radio, etc. They won't last a year even on a tender.
I went up to the rubber store and had them cut out some. When I wanted a bit more preload, I had some thin ones cut and added them. When they asked what it was for, I told them mounts for an air compressor. I don't think they would have done it if I had said experimental airplane.
Something that you get used to. Least for me. I didn't get really queasy until I went up with a retired Air Force pilot in a Christen Eagle. After a roll, a snap and a loop, I was getting pretty quiet. He asked me if I was okay. It was then I realized that I had forgotten to tense my abdominals while doing a restricted exhale. He then went on with his routine flipping that plane around all over the sky. It made my ride in a P51 and T6 seem docile. One of my friends is an ag pilot. Put him in a small field with a lot of turning, he would land, get out, and puke. He started using a patch and he said that helped a lot.