IDD CI24 ECONO MM Penta 1.20 Galaxy II 1.2Mtr Polar MTG yes it has been on the arc for 25 years and is now fixed on 13 East using two pairs of rusty molegrips. Unlike me they never groan but always perform.
If I understand correctly you want to run your digiboxes off a 12v supply.
There are two ways to do this. The first is to buy a 12volt to 240volt inverter and then plug your digibox into this. They do consume a lot of power this way though - watch out for flat batteries.
The second way is to not use your old digiboxes but try to find a Pace Minibox. There are plenty on Ebay _http://search.ebay.co.uk/search/search.dll?from=R40&satitle=pace+minibox or try the small ads in the newspapers. The Minibox runs directly off 12volts and normally comes with a plug-in mains adaptor to supply 12volts. The Minibox is much more efficient in its use of electricity so the battery sould last longer.
I don't know the digibox but this is valid for everything, you can always by-pas the 220v internal power board an plug DC directly into the main board.(you may have to adapt the different DC levels ex. 5V,9V... but that is easily done with a simple IC)