As far as I know only the 88s came with the straps in the trunk. Although others might have them as well, the ship through cars (CJB) had the straps for sure.
The area behind the seat is nearly the perfect size for the t-tops, but I found I need all the seat travel I can get so I only do that on the passenger side.
The t-tops will not fit under the hood of a stock Fiero. At least not both of them at the same time, along with the spare tire and jack. That's not to say you couldn't modify the forward trunk to accept the t-tops but I have yet to see that done.
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88 GT T-Top, 88 Fastback Chop-top (Archie #14), 1984 Indy, and 88 Chop Top T-top
Firebird Interior Installation Website