The older style rock screen has 2 aluminum support arms that slide one-within-the-other. There is no spring or shock. There is a wing screw that locks the arms in the up position. My 1980 Bigfoot
and 1973 Compact Jr have the same rock guard supports.
I doubt we will ever know when Bigfoot
added reinforcement to the roof since it's hidden in the ceiling structure. Any company that has been in business since 1978 has made hundreds of changes, large and small, as they improve their product. I look at my Bigfoot
and others and wonder; when did they move the closet, add a cover over the propane
tanks, switch from wood grain vinyl luan wall panels to real wood veneer, add an exterior grab handle, add exterior storage hatches, etc.
P.S. I will always call my trailer a 1500 series.