The cheapest solution is to replace the struts with stronger struts, if you have a look at one of your struts, you will see a number on the strut with N after the number, eg 300N is equal to 30kg's I replaced my struts last year and went from 30kg's to 40kg's and lifting to roof is now easy as, I purchased mine on Ebay about 1/3 the price from a caravan spares shop.
I replaced ours a couple of years back for the same reason, fitted a solar panel.
As ours is a large pop top I went one grade heavier on the back end & two grades heavier on the front which is where the solar panel is, fixed the prob.
As stated there is a ID no. on the struts.
JC.
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