PANELS:

Works are either produced directly on your wall, ceiling or floor, or else on a installable panel.  I typically use MDF board, but I always take the environment into consideration when choosing the material.  A few trompe l'oeil artists use canvas, but canvas must be mounted and stretched properly, which adds time and expense.  Also, a mounted canvas produces more shadow line (see below) than I like.  There is also an increased danger of damage to the work.

Advantages:

There are actually several advantages to installable panels, and I prefer to work with them when possible.  In the first place, they are more economical due to savings in travel time and gas.  Silly of me to worry about gas prices in this day and age, I know, but I can't help it.  I like to keep your costs down.

I am also able to control lighting, humidity, and other aspects of working conditions that usually allow me to finish the project more quickly.

Finally, should you decide to move, you have the option of taking the trompe l'oeil with you.

Disadvantages:

Sometimes the subject matter, or the space itself, does not lend itself to panel work - it must be painted directly onto the surface.  For example, existing floors have no recess to receive a panel, and a panel laid on top would be a safety hazard.

Also, panels that are smaller than the space can produce a shadow line.  In some cases that's fine, and in some cases it would be distracting.  Trompe l'oeil windows and doorways are good subjects for panel work, since the molding would project a shadow anyway, but the illusion of a break in the wall would be painted on directly since there can be no shadow line.

PAINTS:

I choose the paint based on the environment.  I most often use latex-based paints.  They are generally durable, versatile, and hold their color well over time.  I can use them in glazes, or in thick impasto effects.  They can be mixed with other materials to increase their versatility, and they dry quickly.

Exterior walls sometimes require specialized paints for strong adherence and durability.  Happily, there are an ever increasing variety of media for this purpose.  These specialized paints have been steadily improving over the last 20 years.

FINISHES:

If the trompe l'oeil is going to be exposed to weather or traffic, I will apply a clear finish that protects the paint, while not changing the color or reflectivity. If the work is going to be on the inside and not walked on, etc., then no extra coating is required.