There's all sorts of ways to visually simulate the look of open faced neon channel letters in CorelDRAW.
I design the ones we build to exact specification so the letter backs & faces can be routed and the tube paths can be used for neon tube patterns. Then I concern myself later about how to make the artwork look for client sketches. I start with a full size layout. Depending on the size of the letters and the lengths of the tube paths I'll make the thickness of the tubes 10mm, 12mm, 15mm, etc. The edges of the tubes have to be a certain minimum distance from the edge of the returns. I'll create a center-line path for the tubes and use the pen tool settings to determine tube thickness. I'll keep the center-line path and make copies to convert the object to outline. For client sketches you only have to do this a couple or so different times to create a decent looking glow effect on a scale drawing. Using tons of outline or contour steps is overkill for a scale drawing. If I want to be really picky about the look of it I'll take the paths over into Photoshop and dress up a better looking rendering there. Some of this just really depends on the specific project.
Single stroke neon in channel letters can be a pain to produce. This is where the blend tool in CorelDRAW can be handy. You can break apart parts of a letter and then blend between the parallel lines to create a single stroke line in the center of the letter. You'll have to reverse path direction on one of the outer parallel lines of the letter shape. This method works best/easiest on clean, sans serif letter styles. With some of the more irregular typefaces out there you'll be stuck having to hand draw the single stroke, center path. The blend tool can also work for creating exposed neon for really large letters where multiple tubes are filling the open space.
Currently CorelDRAW does not support gradients on path strokes. Adobe Illustrator added this feature a couple versions ago. This feature can create a convincing looking neon tube effect just with one open path. Maybe some day Corel will offer the same feature in DRAW.