I've done what mep has said at 2 different washes of mine on Coleman canopies, except I just installed 2-4' bulbs the length of the 8' canopy (as opposed to 4 which would replicate the 2 -8') ... they give out plenty of light...
They make a conversion kit to turn the 8' fixture into 2- 4' one (it's basically a metal mount with a spot for 4 tombstones that you install in the middle of the 8' fixture)... take some pics of what you have and take it to an electrical supply shop, they should be able to help you out.
I went with a brighter kelvin as well