Jerry, it sounds like you're rear slides are similar to mine even though we have a king bed and you probably have a queen bed (based upon the 38' length).
Here's my first modification -
I removed the 2 - pieces of plywood that form the base. Ours has a wood platform at the head end that travels in & out with the slide. You'll have to cut a hole in the plywood to allow distribution of the air tubes. I then determined that the air pump is too tall to simply sit on the platform under the head end. I added 2 X 2 strips of pine to the top of the frame (wood on metal) and re-installed the plywood. The extra height was not a comfort issue but the vanity slide "squeezes" down on the foot end of the mattress somewhat. It didn't seem to hurt anything so we kept it that way for more than 2 - years.
Issues / Problems -
Since my wife finally retired and has spent considerably more time in the coach, she pointed out that it always feels like you "roll" out of bed on the edge and the sheets don't stay tucked in under the mattress. The problem was that the plywood base was NOT as big as it needs to be to adequately support the mattress. We were also becoming more concerned with the "squeeze" affect on the foot end of the mattress possibly deforming &/or damaging it.
New Solution -
I removed the 2 X 2 strips to lower the mattress back to its original heigth. I then cut 2 - new pieces of plywood large enough to actually fit the mattress.
Here's the interesting part ... we looked high & low for some material to cover the edge of the plywood like the original pieces. It turns out to be "hull liner" material used on boats & RV's. It's the same material used for the ceiling of our coaches. We couldn't find the exact color but found something suitable (the bedspread covers it any ways).
I mounted the air pump right in front of the platform where the AC cord still reaches the outlet and the air tubes reach the mattress. I purchased "L" shaped brackets and flat aluminum strips at Lowe's. I don't have a picture but it looks like a wide "U" with an ear on one end (inverted "L"). The "ear" end screws onto the platform while the other end screws into the wood cross member. I made 2 - such brackets and mounted them to support the air pump. I used some double sided mounting tape to keep it from sliding around. I should have done this the first time!
Sorry I don't have pictures to post. NOTE: There was some drilling involved as the brackets were predrilled which didn't match when you but them together back-to-back. I can make a diagram and post it if necessary including parts. Feel free to message me with any questions.
I hope this is helpful.