One of the better options for MDF is to use a durable outdoor weathershield intended for wooden exterior doors. You will not need primer as the paint goes on thick (though you will need several coats), plus it makes the surface less porous (so more resistant to water spillages), the finish can be amended based on the number of coats you use (2 for matt, 3 for semi-gloss, 4+ for gloss) and it is easy to apply (foam roller for best finish). Sadolin make an 'ebony' colour of this paint and it is readily available at most garden centres:

Doesn't matter whether you use the standard (pictured), the 'extra durable', or the one coat (red tin) stuff, though they do cure at slightly different rates (original tacky after 6 hours, 'one-coat' tacky in about 3 hours) and it is best to leave 24 hours between coats. It's quite pricey at around £30 a tin, but you can do 3 coats on 2 full-size uprights using 1 tin, so works out to £15 a machine. This is very similar to what we use on our machines (though we use a bulk-buy paint) and we have used this on full machines in the past and as a touch-up paint for our cabinets: