I guess I was the only one who was thinking that with a mini trailer comes a mini budget.
$1000 for a DIY Fiberglass tub kit? To rich for my blood.
I believe the $1000 he talked about included the trailer itself and the toneau cover for the tub along with the tub kit. From seeing his other projects, it would be a first-rate trailer.
This trailer as you see it here cost about $1000, and it's definitely not waterproof. But it is set up how I wanted it using what skills and abilities I have. That's the beauty of these little trailers - they're like Jeeps. You can build and modify and set them up however you want to. You can go cheap, or drop some money on them. And I want to see what folks have done with their little trailers (so post your pictures!).
What do they say? - "To each his own".
If you're wanting to go inexpensive (and that's legitimate) or have a mini-budget, you can get one of the red 4' HF mini trailers with 12" rims/tires for about $200, and then add another $100 or so for a plywood floor (half of a 4'x8' sheet), 1x4 slats and nuts/bolts and it would be ready to roll with a little bit of cutting and drilling the lumber and putting it all together. Using scrap lumber (like from a section of 6' fencing made up of 1x4 or 1x6" pressure treated boards) might get you in even cheaper. You might be able to make a metal trailer tub out of an old refrigerator - and use the door for a lid (I'm eyeing my refrigerator as I'm typing this). If you're on a budget (no shame there that's for sure), get creative! Have some fun with it! Think outside the box (pun intended).
Bolt a spare tire on there and you're even more set. HF has spares on sale sometimes under $40; I've got two 12" spares (one's never been used) sitting in my garage that I'll sell cheap if anyone wants one. Heck, I'll give you one if you show up at my house pulling a little 4' trailer behind a Jeep ("...while supplies last").