If you do go with JB Weld (saw you bought some form of compound) you have hours to get it right before you are too late. You want the slowest drying compound you can find as the slower it dries, typically the harder it sets.
I put a layer of it in between rifle stocks and the metal receiver/barrel to make the stock fit like a glove and flex less. While I do use a release agent (kiwi shoe polish, nothing will stick to it) on the metal to allow the barrel/receiver to come out, after 8-12 hours the jb weld has set up but is easily cut with a razor blade. If you needed to adjust you still have time to undo and remove everything. Keep a bottle of solvent on hand as well. Acetone/mineral spirits/etc all dissolve the compound so if you have any excess, mineral spirits on a lot of Q tips makes for accurate clean up work without interfering with the compound you want to stay.
If you want it to be something that will never, under any circumstances, come off, you need mechanical lock. With wood rifle stock you drill angled holes part way through (but not fully). When the compound fills these holes it creates a lock. with just a flat surface of compound, the right impact can crack the bond and cause the compound to let loose. If you have these angled cavities, now the same impact is absorbed into the compound rather than against it. If you put the angles opposite of each other you lock the compound.
So keys are:
Take your time, you have plenty of it
Cover everything you don't want compound to stick to with Kiwi shoe polish (use clear, the colored kinds can stain).
Be a little heavy with the compound as the Qtips will clean up any excess well
Have a FULL box of Q tips, use them once only and toss them away. You don't use the same TP to wipe twice, don't use the same Q tip
Use a solvent to clean up anything (while the compound is still wet) that spilled.
After 8-12 hours check on consistency and trim with a sharp razor blade. After 24 hours you can use a sanding disk on a dremel as well, but I've found the cleanest looking edges come with a steady hand and sharp thin knife.
Good luck and post some pics when it's all done.