"am i ok to secure my shower tray to floor boards on my bathroom floor? if so would it just be like pink grip or something similar."
Of course you can - if you want it to move, probably crack and have leaks all over the place. The answer is NO - follow the manufacturers installation instructions. If its a stoneresin tray then remove floorboards and replace with WBP ply, bed the tray on a sand/cement mortar bed. If is a plastic thingy with those horrid feet (no I don't like them one little bit - grin!) then again make sure you have a stable surface on which to mount it - remove boards and reoplace with WBP as before.
personally i'd be inclined to remove the floorboards and replace with 3/4 inch ply to give a flat base (assuming here that the joists are true).
seal the wood with an acrylic or latex primer then stick shower tray down. i'd use silicone rather than grip fill - you don't say what type of tray it is, whether it's resin or plastic. don't use the pink stuff if it's a plastic tray, it will melt. you need to use yellow grip fill on plastic as it's solvent-free, though i'd still use silicone rather than adhesive.
many builders merchants now sell this stuff that they call 'builders adhesive' or builders sealer or various similar names that can be used for fixing shower trays, general sealing and adhering. never used it myself, it sounds to me like just another way to market silicone :) - though they reckon it can be painted. only reason i mention it is that it does state on the tube that fixing shower trays is one of its uses.