Will a topper from 2001 3500 fit on a 2003+ 2500 or 3500 long box? Any difference in the 3rd gens on the interior measurments between a SRW and DRW?

Any changes in interior box dimensions between the 2rd gen and 3rd gen?

Had a second daughter recently and am finding it difficult to fit 2 car seats in the back without moving the front passenger seat way up. Daughter #1 not yet big enough for a booster, second daughter is newborn and in a rear facing bassinet. I'm remotly considering going to a 3rd gen for the bigger rear seat(not a mega). When I bought my '01 the topper and camper I had that was on the old '92 did not fit the 01's box, tapers at the back. Just wondering if I go to a 3rd gen if I'll have to go thru all that hassle again.

Really don't want to as I just finished upgrading this one and getting it the way I like it! Thanks!

 

i think and this is just from looking at my dads truck that the box has what looks like a bow in the middle but this could just be my eyes playing tricks on me too.