I am a Dremel wizard, not much of a boast - but there it is!
I could put a little tutorial on when I get time.
I use a lot of Solido castings as well.
The secret is not to try and cut, but, using your dremel or small electric hand drill with an HSS bit, say, 0.75mm, drill a series of holes around a line just inside the eventual opening line you want. It is best if you use a punch to make a series of pilot holes first - stops the drill bit from skidding off and marking your model.
When you have drilled all the way round, simple knock out, or pull out the panel with needle nosed pliers or similar. Make sure you drill enough holes or you can snap the models when yanking out the bit, although that would take some effort with Solido. They are not called
Solido for nothing!
Then use a flat metal file to tidy up the edges.
I managed to snap a Morris Quad in half this way, which then gave me the idea of using the remaining front end for something else. The resulting MAT was well received by its new owner after I extensively scratch built a new rear end -so alls well that ends well.
Hope this helps.
Do you not find Solido a little on the large size and out of scale - there Tiger is enormous for example?
A SOD - Sawn Off Daimler - as driven by The Devils Own - The Inns of Court Regiment. (again use of a damaged casting)
Some Solido M20's in progress - sold to a guy in US