Is this very large flat panel printable in ABS? I am designing an part for my car. It is a panel for the rear door. I want to add it some cases for tools, but before going on, could you tell me:

It is a large flat panel, around 100cm by 35cm.

Is it going to be suitable for printing in that ABS material? Is it too big?
ABS would be fine, as a material, for the application.

The problem, given the scale, would be the printing device used. I would suggest that you have the piece cut to spec for you using a polycarbonate. 

If you have access to a workshop you could do so yourself if you set up proper fencing using a larger sized bandsaw(with a very fine toothed blade), had rollers to help support the size of your piece(as it would not fit on the tool's platform) and likely need a second set of hands to help control the outfeed. You would also need to drill access for the cut out then cut the perimetre.

You could also consider printing(ABS) in smaller sections then fusing each section together edge to edge(solvent welding of ABS is very strong and permanent), if you were really dead set on using a typical 3D printer for this. It would, in theory, be possible, but it would be very tedious. The adhesives, and cleaner, would be available from any plumbing supply and/or (home depot, lowes, walmart et al.). If you go this route be sure to have ample ventilation and plan your work space well in advance. I would not recommend this option but it is "possible".

Given the scale of the piece though, and for sake of accuracy, going to a shop with CNC equipment and using polycarbonate would be your best bet.