John Riddle's book "Canadian Pacific Color Guide"
has a picture of 41' 6" flat car # 307694.(straight side sill)
In the Maintenance of Way section there is a photo of
# 312705 (fish belly side sill) 41' 6" idler flat which was
converted and renumbered from a "trailer flat" (TOFC)
in the 3065574-308125 series.
One of those 2 photos is probably what you are looking for.
Is the 300800 series straight sill or fish belly sill?
What year(s) are you interested in?
Does anyone have a picture or is there a web site with a picture of a
CP 41'6" flat car in the 300800 series.
Thanks