Hi Rob

If you are mixing MEK in the  resin  to make it cure, it is  polyester  resin  not  poly uerethane
and  the  answer  would  be  yes  it will work as  a fuel proofer. it will not  however  cure  over  epoxies of  most types, so you need  to be  careful there

Randy

Hi Ron

 Your welcome, I used to use polyesther  resin a lot, they are  thin  and  very easy to spread and paint inside cowlings,pipe tunnels  and  of coarse  glassing  cowling  and  front ends, but  with the introduction of the
polyamide resins (finishing resin), they are  thin easy to spread, and  so much more  friendly  to  work with,  plus  the ones I use  mix  1  to 1.
if you have not tried them  I highly  recommend  you  do.
Hobby Poxy  and  ZAP  makes  them,  along  with  the  BOB Smith  line  of  epoxies

Regards
Randy