You can use mineral spirits to thin.  I would use a better quality product, not the 99 cents per gallon stuff, but even that would work.  333 is a thinner/retarder, and it slows drying allowing the product to flow out better.  I use 333 with Epifanes when I varnish brightwork on my big boat in the summer, otherwise I use Epifanes thinner, which is just a higher quality thinner.

Wholesale Marine ships 333, and they got mine to me very fast--so that's an option if you can wait a couple days.

I used Schooner Gold on my first kayak and initially struggled with it.  In the end I used a combination of 333 and Penetrol to achieve a nice finish.

Cheers.

I took BankerBob's advice and have ordered some Interlux 333 (half as evil as 666?) via mail order. The straight Gold left such a rotten finish I now need to sand it down with 120 grit and > to get the brush marks out. It takes about 4 1/2 hours to sand the Peeler interior with each grit. So I've another 8-12 hours of sanding before re-coating. I'm totally out of interest in any shiny objects again. My next boat gets a Sam Devlin truck bed liner spray job. My Peeler has proven that time can be stretched to infinity, or at least twice as long a building time as estimated on the plans. I know, I know ....stop whining and sand.