As 12am said, Orange Peel is caused by improper atomization.
Atomization is the process of breaking the liquid into small droplets.
With a spray gun, the cause is either the liquid viscosity is too high or the air pressure is too low.
The corrective action is either thin the liquid, or increase the air flow--since it is the air flow which breaks the liquid into small droplets--or a combination of both thinning and increasing the air flow.
A third cause of orange peel (improper atomization) is wrong tip size.
A fourth cause is poor quality spray gun.
I mentioned these things so you would get a better understanding of the cause, even though you are presently using rattle cans.
Aerosol cans will give you disappointing results, but some are better than others.
The actuator/nozzle style on the left is likely to atomize better than the one on the right. The left one also produces a "Fan" spray, while the one on the right produces a "conical" spray pattern.
This one also allows for adjustment of the fan spray, by rotating the light blue center, to obtain a vertical or horizontal fan spray.
The better quality aerosol tip can help to a certain degree.
Unfortunately, the two tip styles are not interchangeable.
Wet sanding has some benefits--less gouging and distorting of the surface being sanded and less heat buildup.
Wet sanding can be done with water plus a drop or two of dish soap in a mist spray bottle.
It can also be done with mineral oil found at your local pharmacy.
The wet lubricant needs to be removed completely before any additional topcoat is applied.
Soapy water can be wiped repeatedly with a damp cloth, keep rinsing the cloth.
Mineral oil can be removed with a solvent, such as denatured alcohol or mineral spirits (paint thinner). Just make sure don't use the same solvent used in the finish, or you risk re-flowing the finish.
Oil based Polyurethane uses mineral spirits, so a denatured alcohol-dampened rag would be a good choice, because it won't re-flow the finish.
Denatured alcohol is the solvent for Shellac and lacqer, so mineral spirits is a good choice for wiping these finishes after sanding.
Another option is to use stearated sandpaper, which has a soapy lubricant added to it. It would have some of the benefits of wet sanding when it is dry.
If you are using water-borne finishes, stearated sandpaper is a bad idea, because you risk adhesion problems, should the need arise to apply another topcoat.
So, if orange peel is unavoidable, wet sanding is required.
Speaking of sanding, you should know that sandpaper grading is not universal.
The US system is called CAMI, while the European system is called FEPA.
I mention this, because you might have or at least see some sandpaper which has a "P" preceeding the grit number, such as a "P180" grit.
I've got some of both. It's increasingly common.
At the lower numbers, the two systems are pretty close--180 is the same as P180, for instance.
But above 180 grit, the two systems begin to show significant differences in the way they are graded.
So, if you had sanded to 360, then went to P400 or P500, thinking you were going finer, you went the wrong way. You went coarser.
It's just something to be aware of.Here
is a chart which compares the two systems.
I could go on about finish problems to avoid, but I think I've been too long-winded already.
Oh, here's a finish problem you can avoid.
You can lightly sand and apply another coat after the previous coat has flashed off (dry to the touch, but not fully cured).
But, whichever side is face-down might get little dents in it, even if the resting surface has a smooth terrycloth towel on it. That would get you billions of little dents in your finish while you are sanding the opposite side of the box.
This is where a paint stand comes in handy. You can sand on the same stand you are painting the box on.
I could go on, but I'll spare you folks instead.
Sorry about the long post.