Can't get a warm enough hotspot on aspen.

I set up a small rack with some heat tape with the t-stat probe directly on the heat tape, and the bottom of the tub on the hot spot gets warm enough but the aspen above it does not feel warm enough. Is just heating the bottom of the tub good enough?

What are you using to measure the temps? If by "feel" you mean "to the touch", that doesn't work because your hand is 98.6... so a hot spot of 88-92 would feel cool to you. The best way to measure actual temps is to use a temperature gun. That way you can just point and shoot and get temps for on the bottom, on the substrate over the hot spot, the substrate on the cool side...
You want to bottom of the tub to be 88-92. The top of the substrate will be cooler., so use just a thin layer over the hot spot. Your snake will burrow down and you don't want the bottom of the tub too hot because your snake will get burned.

By warm, I mean relative to the cooler side, but yeah probably a little too hot. No animals in there yet, so don't worry. I have some thermometers with probes coming in the mail soon. I'm pretty sure I have a temp gun somewhere, haven't seen it in years though. lol

Find that temp gun; it's your new best friend, after your t-stat. What t-stat are you using to regulate your heat tape? (And hey, welcome to FC!)

Temperature guns and thermostats are great, good advice, but why are we saying that the hot spot should be 88-92 degrees without knowing what kind of animals are going in there? Many old world snakes will die from that kind of heat, and I keep three species that like it warmer than that. What kind of animals are going to eventually be in there?

Omg. I thought it was a BP. Do t know where that thought came from.
Good save, Elena.

No I know how it is. Most people are talking about BPs when describing a rack, so it's an easy mistake to make. I also almost made the mistake of assuming, in my post, that it was snakes, as opposed to geckos or something, though I don't know what kind of gecko would live on aspen.

Couldn't find the temp gun so just ordered one.
Looking at getting a couple milk snakes, sinaloans maybe, and a cape or baja gopher if I can find one. I know cape gophers like it a bit cooler than sinaloan milks (if what I've read is correct), and was thinking I could just put something in between the tub and heat tape so it doesn't get as hot as the other tubs, or maybe just remove the heat tape from one level, since I've read they do better without heat.

Sinaloans do best with a hot spot around 85, and a night time drop of at least 5 degrees. I've never worked with Cape Gophers (but think they are really cool), so I can't say much about that. You might try checking if Jason Nelson has any, he breeds many Pits.

I remember seeing that name a lot a few years ago in the pituophis section of market.kingsnake, haven't seen his ads around for a while.