I have an old Honda Pilot and it has bare roof. Ideally I would buy a roof rack system to transport kayak but since I will be buying a new suv the beginning of the next year I really don't want to put more money on it.
My question is that if it is safe to transport kayak (possibly a Big Tuna or Hobie) using one of those kayak form blocks that you see at Academy. Does anyone have any experience using those high density form blocks?

I think it will be too much for a bare roof. If it had some type of luggage rack
you may be able to put the foam on the cross bars. You will still have to be able
to ratchet the kayak down tight enough to the roof, which will cause it to push
into the roof even more and make the roof cave in.

It is fine for the Kayak. Not the best for the roof of the car. If you aren't too worried about a couple of dents on the top of the car then that's the way to go.

I have a piece of [censored] Kia Rio and didn't want to pay to put a rack on it. I bought a sheet of high density insulating foam and cut it into strips that were four feet long by about 5 inches wide. I glued them together to make 5" by 5" foam blocks and have been using them for years. The roof of my car bows a little under the blocks but the kayak does great.

If you use foam blocks, place them near the windshield and back window. The car frame is reinforced along the roof edges - at least more so than the middle of the roof which is about as thin as a beer can.

Where did you buy the sheet from? Is it as dense as the one for kayak?

I use the Acadamy foam blocks and as stated above place the foam close to the frame on the wind shield and back window or hatch . I have a Pontiac Vibe and carry the Pescador 12 on it.

I haul my Pescador 12 upside-down on my truck cap laying on two giant pool noodles with PVC pipe(1"?) in the middle. I have two bungees that go over the bottom of the Yak and hook into the ends of the PVC pipes. That secures the noodles to the yak. After the yak is laying on the truck cap, I strap the yak to the truck with ratchet straps. If you are going far, it helps to run the front strap thru the scupper holes in a loop. That keeps the yak from shifting from side to side. I've been doing this for years and have gone great distances like that. I have to replace the noodles once a year, but they're cheap. f you are diligent in strapping the yak down, you shouldn't dent your car roof.

IslandJim

Economy wise . . . almost anything will work . . . but . . . safety wise . . . be very careful.

A kayak flying off of a roof could be a very dangerous situation resulting in loss of lives and humongous lawsuits. Is saving a few bucks worth the risk?.

I bought it from Lowes. It's what you would use for drywall insulation. Works fine.

I use pull-tight straps and once I've tightened it down you can't move the yak without moving the car. I've taken it to East Texas and back several times with no issues. In addition to the two straps over the hull, I do use a strap on the front connected to the tow-loop as well as one on the rear connected to the tow-eye as an extra safety precaution, but I would recommend that no matter what type of towing rig you had.

The way the roof of my car is built, it causes it to bow a little in the middle over the drivers seats, but I don't really care and it pops right back. There are better options out there for most, but for me it works just fine.

I use the Yakima foam block system and it works just fine. Just be sure to use the fore and aft tie downs. I run at highway speeds without any issues.

I would see if you can find some factory side rails at a junkyard or search ebay/CL/etc. Then get some yakima/thule or equivalent bars and secure to the side rails. When you get your new ride, you can take the bars with you and use on it...the most you lose is the side rails. As MikePaddle said, not worrying about your yak coming off (and the ease of loading) is worth the small expense IMO.

I wanted to keep my travel box and any yak I might carry as low as possible so I didn't use the normal yakima "feet" but instead hard-mounted the bars to the factory rails. I can't adjust them fore and aft but I located them at a good position for anything I might carry. The factory bars were not confidence-inspiring; the yakima bars are rock solid mounted this way. And pretty much theftproof. If you look close, you can see the mounting I did here:

Here's a better pic - maybe this will give you some ideas: