>>>> I tried exterior poly thinned about 1/3 to make wipe on. The exterior poly has UV inhibitor in it.
If you used a big box brand of exterior poly, you will get very little UV protection and what UV protection you get will be short lived. Polyurethane is quickly damaged by UV and should be avoided where UV could be a problem. As the UV protectorant absorbs the UV it is itself destroyed. Even true marine non-poly exterior varnishes need sanding and re-application every year or two. Big box brands of exterior poly have a relatively small amount of UV additive. By thinning it you have further reduced the effectiveness of the remaining UV protection.
The UV protection added to finishes is there to protect the finish, not the underlying wood.