Difficulty setting up terrarium

Hello all! A few weeks ago I purchased a water dog, and without missing a beat he is already starting to morph. He started in a 20 gallon, and when he began breathing I moved him to a super makeshift 90 gallon lifted so that he could have a shallow end and a deep end.

Of course this is an unacceptable habitat! Because I currently have no real room for my 90 gallon, I have purchased a 20 gallon long (so it is 30x12). I am having some extreme difficulty balancing funds with a set up that will give my little guy enough space to swim and still be able to get to some land complete with coconut fiber/top soil mixture.

I started trying to use gravel to make a ramp as well as a *base* for the land, complete with a makeshift divide. He was unable to make it up the gravel to land (I saw him struggling with pebbles multiple times but ended up just clawing them away from the original ramp structure) I tried adding a little extra water to help aid this issue but ended up with the substrate just absolutely everywhere.

Round two! I went and purchased a bowl the I designated specifically for substrate.. but it does not weigh enough and wants to float in the water, further messing up my makeshift ramp (at this point I thought if the gravel covered the floor it wouldn't shift as much).. A few pointers I should mention - While I understand gravel is dangerous, I did purchase the biggest rock size I could manage and I hand feed to try to avoid any incidents.

But I am absolutely at a loss for how to set up his vivarium, especially without breaking the bank (Since I'll have to get a whole new set up again in a few more weeks) So any help would be so ridiculously welcomed. Thank you (for taking the time to read this extensive post, first off)

You could always just have the tiger morph in a separate container and move it to a terrestrial tank when it's completely done morphing.
As a morphed adult the water area would really only be a waste of space and some people say that they're more prone to disease when housed semi-aquatically.
Checking out these articles might help too:
http://www.caudata.org/cc/articles/tiger_sal_101.shtml
http://www.caudata.org/cc/species/Ambystoma/A_tigrinum.shtml

I've read both, and they have been awesome articles! (I'm a total newbie to all of this)
I guess I'm just curious... Shouldn't he be offered substrate to burrow? He hangs out A LOT in the shallow end with his head perched; but as of right now he has no 'land' to come up on and hide.

The final tank should have a substrate of coco fiber, or organic topsoil(no fertilizers) or a combo of both. I like to have a slope of it of around 4-8.5inches. Once its done morphing just move it into an adult tank but for the morphing tank any land would be fine, just make sure it doesn't build up waste like a gravel slope, putting a hide on it might help encourage it to go out of the water too.

Once he's morphing, I'm home free. I've done so much research on how to keep him - to the point where I'm thinking of making a very small undergravel filter for his soak area once he's in his final home. I have just been unable to find any information on how an inbetween tank should be set up. Even with scouring these boards- I found I'm either doing a terrible job at finding old posts or the information pertains to something other than husbandry. But great to know! Thank you. Went out and got some slate and quarts (passed the vinegar test) and used that as more of a stacking agent, a ramp and a solid piece of land. And don't worry, he definitely has hides both for inside the water and out.