I have used 3 non skids over the years that worked ok. 2 have clear options.
Non skid tape 3m brand amongst others, is available in clear by the metre, clear is often used for bathtubs etc. so can be found in some hardware and plumbing stores. There is a Austalian made? (or packaged) tape that is cheaper than 3m almost anything is, that I have now had on "Thrice Bitten" for 4 years and is doing ok.
Rather than sugar in resin or varnish, I would recommend salt (just make sure it's not too humid when applied as it can become damp and effect the cure). I have used this on sailboards and gunnels in whatever paint resin etc. i was using. Gives a finer non skid than sugar, just sift it before applying.
Final one is not available clear, but I found worked well and that is K&H pool deck? paint. Commonly painted on to concrete but works on anything, is water based so has no compatibility problems and dries quickly. Can be tinted what ever colour you like and is cheap (but not available in small tins). It is latex paint and has granulated latex in it, whick makes good non skid but not abrasive, has to be recoated each season as it wears away (but doesn't wear you gear) but like I say a can is cheap and lasts a long time.