Double skinned or box type covers were developed to span large openings. They provide equivalent strength to those with open construction without protruding so far down into the cargo space and losing cargo carrying capacity.
In my opinion, the sentence in question "They provide equivalent strength to those with open construction" means "They provide the same strength as those (covers) with open construction" or "They provide equivalent strength as compared to those with open construction".
I think the first version is correct.
http://pl.scribd.com/doc/38580051/Ho...d-Hatch-Covers PDF format, page 8
In my opinion, both are correct because both have the same meaning.