Do I need to heatsink 10W resistors?

I've got some 10W resistors that are dissipating close to their maximum power rating. Should I be heatsinking them? They're not the aluminium cased ones, they're the white ones that look a little bit like chalk...

Also, since I have to have an array of these resistors is it alright to pack them right alongside one another or do they need some space to "breath"?

Are they the ballast resistors for the wheelchair, forming a 0.7 Ohms?

If they are running at their maximum ratings it is good to use a heatsink, it is alright to pack them right alongside, but I'd recommend you not to exceed 75% of the maximum power rating.

yes for the 0.7ohms resistor combination. How do you heatsink them though because they're not made of metal? Just strap them against a metal plate?

(I was using the 25W aluminium ones but I see now I can just use more of the 10W ones at a fraction of the cost)

They need considerable space to breath, and if they are running anywhere near their maximum ratings they need to be protected so no one can touch them, as they will be a serious buring and fire hazard.

Yes, just wrap/place them on a metal heatsink, using thermal paste or thermal glue. Leave some space between them, like Nigel said.

I'd use 14 10 Ohm resistors, in parallel, to get 0.7 Ohms. So that you divide the 75W among them, each one will dissipate about 6W in this configuration and, individually they won't get too hot, but the whole pack will dissipate 75W, so they will get as hot as an incadescent light bulb. (75W was stated in the schematic posted on the other thread.)