You could use a longsleeve shirt (not to thick) and try again. This will give you an idea of how it will fit with undersuit.
Also u can use padding foam inside to prevent sliding.
Do you perhaps have some pictures, so we can see how it fits you?
Hi Gary,
I'm about 6'2. Don't have a RS (yet) but it should fit you nicely! Did you go for the kit or fully build? Sometimes fully build needs some tweeking.