What kind of wood is it? Bare or coated?
If you're just looking to coat it, you can use Minwax Polycrylic. If you're looking to pain it, check outdoor paints. I used Valspar 365 outdoor paint/primer blend from Lowes that's water/mild/moldew resistant and water just beads off. Make sure you let it air out for a few days before putting your Cham in.
Also be sure that you fill in seams where the wood meets. The outdoor paint will fill it, but I was extra cautious and used GEII clear silicone on all the seams and then painted over it.