sorry if you know about this,
I tired this technique last night and it works great
if you have a hull from an old kit the hull no doubts
has the holes in the base were the motor unit went
to fill these get some plastic card and cut it down to
the size of the holes and glue these inside the hull
so that the holes are blocked off. allow the glue to dry
get some fast bonding resin that is used for car body repairs
this can normally be sanded in about 30 mins. mix it with
the hardener and dip a cocktail stick into it start to fill up
the hole once it's filled up spread it over a little do this to all
the holes and allow it to dry fully once dry just sand it down
and it's nice and smooth it took me about 30 mins to get 6 holes
sanded down. the advantage of resin is that it drys quicker,
more solid and doesnt shrink like filler does

Thanks Mikeli125. I guess I've been luck. Even my old Tamiya kits like the Stuart and Lee don't have these infamous motor holes I hear so much about.. I guess Tamiya has filled them in over the years?

They are becoming less common now... when i find an old kit that has these motorization holes, i do something similar...

1) glue a piece of styrene sheet inside the hull.
2) after this backing dries, fill in the hole from the front side with a mixture of CA glue and MicroBalloons...
3) this will dry in under a minute, and can be sanded in 5 minutes... cheap and fast
4) after sanding, prime and continue building as usual!

Interesting methods.

I put masking tape over the bottom of the hull (on the exterior), and fill in the holes with modeling putty from the inside---let the putty set up and remove the tape----presto---a perfect fill, with minor (or no sanding) needed to blend with the hull exterior.

Steve

HI. I just put some thin sheet plastic over the area(s) on the inside of the hull and then fill the outside areas with super glue and hit it with Zap Kicker. Refilling if needed till I get the surface where I want it. Then sand this down to match the rest of the hull's bottom. Works real well. And the Zap Kicker drys the CA instantly so there's no wating for it to cure out.

Take care, sgirty