Two of the HF square leg carts? No.
Two of the 5dwr HF carts? Yes.
Run end to end.
We called it the "Piggyback" or often the "Land Train" in honor of the three trailer rigs/lorrys they run in Austrailia.
Did it work? Kinda.
The mfg floor at work set a 36" long box limit so a buddy went this route.
Shimmed/mated with welded up connectors between the boxes, and as stated above ran them end to end instead of back to back.
Went about a month and an alternative box was bought.
I, personally, am not a big fan of those square leg HF carts except for very very light duty.
I've seen and had several rack and collapse when stressed beyond mid-range use.
And BTW, if you set a up-armor HMMV armored interior door panel on one, it takes about 30 seconds to begin to buckle , rack and then collapse.
Watch ur toes!!!!!
As "big Z" said, back to back may cause some caster modility issues.
Other than that, give it a try. You can always unbolt and use individually.
Good luck.