Easy Transfix Marker/Gelatinous Cube/Blob...thing!
First, I started with this dice box. Every wargamer has at least one of these things laying around. They come in different sizes and shapes, but this is one of the more common ones. This one easily fits over the top of my Lego figs including the base, and would easily fit any 28mm model.
I then took some crystal clear DAP 3.0 sealant, put it in the caulking gun, and spread it all over the box. I feel I should note that while I'm not aware of there being any hazard to handling the DAP 3.0 after it's cured, if you grow a third eye, it's not my fault.
Using a stick, I gently spread the caulking around the dice box to achieve a rippled effect that I was happy with. Be careful to move in smooth motions and don't pull up on the sealant too quickly to reduce your chances of ending up with big bumps or spikes - unless that's the effect you want.
Once that was done, I set the box on some wax paper to dry. Make sure you do this so it doesn't adhere to anything you don't want it to.
Here's a shot of the inside. You can see that you have plenty of room on the inside of the box.
I liked it so much, I made six more.
So how's look on the tabletop? I've enlisted the help of Gandalf the Grey to demonstrate. Here we see our fearless wizard facing down three orcs and two cobras in a deep dark dungeon.
**WIZ-BANG-CRACKLE** (was that believable?)
That oughta hold'em.
Do not mistake him for a conjurer of cheap tricks!
So that's it. Pretty easy. Somethings I've noticed:
1) While the DAP is stuck very well to the plastic, with some intentional pulling, can be completely removed. It peels off like one of those masks in Mission Impossible. I've tried it, and it leaves no permanent mark on the dice box.
2) The DAP does not take paint well. Again, I've tried this. It looks terrible. If you wanted a blue or green Jell-o looking blob, I'd recommend painting the box with some of that stain glass paint (or some other translucent paint) and then applying the DAP. You might be able to mix the DAP with some ink or something in a cup first, but I have no idea if that'd work.
Anyway, there you go. Let me know if you try this for yourself! I'd love to see what other's are doing.