Yes, you need to have a way to move that water out of the bottom of the tank. It will promote growth of anaerobic organisms that cause root diseases and ensure an excessive volume of gases (CO2, methane .....) that inhibit root function, or worse.

Al

Counterpoint :)

Look up wicking garden beds. Here's an example: http://www.instructables.com/id/Wicking-Beds/

Basically, you'd turn your stock tanks into large self watering containers like Earthbox or others. You just fill up the bottom with lava rocks or gravel until it's slightly above the water spout. Add dirt and water as you normally would. Water wicks up into the garden soil and keeps it nice and moist while the drain keeps the soil from being waterlogged. But there's always an inch or so of water in the bottom available to wick up into the plants. Wicking beds are gaining in popularity since there's no wasted water.

Here's my wicking bed done with a bed of lava rock and fabric bags. They never get watered from the top, only soak up water from the bottom:

Yes you can do a SIP with those stock tanks, but in order to avoid pathogens, you will have to dispose of the media every year and sanitize the planter or sanitize the media and planter every year. You can get away with anaerobic conditions for a while but anerobic pathogen levels will eventually get really high causing problems.

Perlite is good stuff, makes it light and doesn't make you lose root space, or cause drainage/stagnation issues.