Frequently, those RVs with door struts have something blocking the door so you can't fully open it and use the conventional locking system. Frequently, there is an awning support or something similar in the way.
I have seen people install the longer holders (six inches or longer) which MIGHT work.
As to the question about the strut, most of the ones I've seen on CR products are only about 80 pounds. Maybe a 120 pounds would be better. I've also seen folks add metal lanyards/cables to their doors to restrict how far they can open and to protect the strut from gusty wind situations.
Jeff & Laurie -- Full timing in Rockport, Texas
Auggie (our beer-loving English Cocker Spaniel)
Angus (55 pounds of attitude in a 5 pound chihuahua body)
Our home base -- 2018 Grand Design Solitude 375RES -- The "Uno Mas!"
The mobile office -- 2016 Crossroads Hill Country HCT26RB -- The "Poquito Mas!"
Gone but not forgotten: 2015 Heartland Landmark 365 Key West (lost to Hurricane Harvey)