while making my TDQ-Figs, I had some trouble covering up those Slotta bases without making them even higher. I was breeding about this problem quite a while until I had an idea. You'll need some kind of silicone or other moulding stuff (instamould or sth. like that) and some acrylic filler that you can get in any DIY-Store.
First, drop some of your moulding stuff on the structure that you want to see on your base. Wait until it cures and pull it off. No need for a thick layer as you can see...
Than smear a thin layer of the acrylic filler on it and smoothen it with a wet finger. Let it dry and pull it off the moulding stuff carefully.
The filler will remain sticky for quite a while after curing, so be sure to prevent stacking or folding those layers.
Then make a straight cut that allows you to "wrap" the structure around your minis feet and cut out some place to stand
Afterwards use some all-purpose adhesive to stick it to your mini. Since this stuff is very flexible, you can perfectly close the cutting lines and make a very tight fit around the feet of your mini. BUT!!! Don't cover the edging of the base like I did it in this picture. It'll collect the dust off your table ;) Cut it off clean around the edge.
I used cobblestones, wood-plank-floor and a stone wall as a master for these acrylic layers. Here's the result after a layer of varnish (which deals with the stickiness) and some ink.
In the beginning it's quite time-consuming, but after the 5th figure it was getting easier and faster :)
You can also use this method if you have some partial ruins like this...
...which covers only half of the house. I find this looks somewhat odd, so I will simply create the rest of the ruined walls with foamboard and add the original texture with an acrylic layer.
Hope you like it!