There is a Very Simple ways to increase humidity levels in a Vivarium. The simplest Method I found and easiest is to simply run an air line with an air stone attached and blow bubbles in the tank.Here is how I do it.
Equipment used ( Nothing Fancy)
Standard Aquarium Air pump and air hose

Standard Air Stones
On My ExoTerra tank I ran the Air Hose through the Opening in the Top and Behind The Standard Background

And buried it under pebbles. Look closely near the base of the Plant and you will see the air bubbles barely.

And here is a Happy juvenile White's tree frog hanging Out on a Brom.
On One of my Vertical 29 Gallon Tanks I nipped a corner of my glass and Notched the tank rim
Hid the Hose underneath the mosses and just placed the Stone in the back of the Tank out of sight. This Tank is tilted back so a Pond forms in the back

Here is an Adult White's tree frog on his throne all happy
On my other Vertical 29 Gallon did the same

Except I placed the air stone in the back in a simple plastic bowl and camouflaged it. This tank is not tilted.

Here you can see an Orchid that was discounted as dead last year at Home Depot is coming back to life

And a Moss Mixture coming to life.

And the Red Eyed Tree Frog Sleeping away in the Corner. 1 of 3 in the Tank
Nothing special needed nor is it a difficult technique to do.
This a simplified method of using a Canister Air Exchanger.
This Method cost me about US$12.00 for each Tank I do because I use 1 Aquarium pump per tank..and then buy air stones and line. I find the smallest and cheapest pump. I don't like to fiddle buy You could find a Bigger pump and an air manifold and regulate different lines into different tanks from one source.