The desire is there though, that's the main thing :)
I haven't been completely idle though - after spending several hours painting the interior of the tank and experimenting with FW weathering powders, I was surprised (and very happy) with the effect. There's three different coloured earth powders on the flooring, and I even put two tones of rust on the internal doors I modelled that looked great. Then I made a big mistake! For the most part, I've been making a paste out of the powders using Tamiya Thinner as a base, or applying a heavy GW wash on the model and brushing on dry powder while it's still wet. I finally finished it all and was very happy so I did what I always do - applied a coat of Testor's Matt Varnish. BIG MISTAKE!
In the space of 15 seconds, my gorgeously grainy dirt and mud effect turned into a while, flaky ash POS! After I managed to stop crying I tried applying gloss coat over the top (a good solution to the common "frosting" effect when using matt varnishes). This seemed to solve the problem and I breathed a sigh of relief. Then I applied another matt coat (per normal practice) and it went white again! I can't exactly leave rust and dry mud glossy can I? In the interests of wanting to move on, I've left it imperfect and moved forward with building the tank, and will have to experiment more on a test model to figure out what to do next time.
I've posted some photo's below of the interior detailing, along with one of the distractions I've had the last couple of weeks eating a space marine!