Sticking it to a big wooden base and building it up with milliput or DAS or basetex (sp?) or something, is one option. And it\'s probably the easiest.
Another way I\'ve seen it done is sticking the mini on a square/retangular block (Just a flat bit with straight edges - no routering or anything) then building it up - you can easily paint right up and over the edges Then get some of those thin routered strips - I\'m not sure what theyre actually meant to be for - edging probably; beg/borrow/steal a mitre saw and stick them round the edge (frame style) for the final show piece effect.
That\'s prbably more difficult, but for big dioramas it probably works out cheaper if price is an issue... (\"Nothing is too good for my baby!\")
But you\'re probably best off with your plan. Bases are available in various shapes and sizes - Oval, round, square etc... My local model shop has a load and your\'s probably has too.
Burzmali