When determining the size of the strut needed you have to consider the size/weight of the bed you are lifting. You have to keep in mind that the lift is from the back of the bed, not the front. In my case, I ordered 2 ea SL26-150-1
26 is the length and 150 is the output force. It is recommend that both be replaced. As stated/shown they are mounted on the inside of the bed frame and the bed itself.
You can look up the strut you need at this site:
OEM Gas Springs : Attwood Marine
Do a search on the model number you need.
My struts sells for $59.84 for 2ea and they have the mounting brackets you need.