While it’s quite straight-forward to make MDF filler strips on an XL:
Geometry isn’t so kind on an XXL or Standard w/ their essentially square bed.
Making replacement filler strips requires that one do a bit of rotation to make things fit, and source narrow boards, rather than large sheets.
First, go to the local lumber yard and buy a board of suitable dimensions (greater than 40" in length, wider than 3" or so, and as close to the 3/4" thickness as is possible). One option is Azek “Exterior PVC Trim 1 x 4 x 8’ (nominal dimensions, actual dimensions: 0.75-in x 3.5-in x 8-ft)”:
Another option is MDF boards — these are more affordable, but aren’t as thick, and usually are pre-primed.
If you don’t have a truck or van, bring a handsaw (or buy one while shopping) and cut it in half or so that it will fit in one’s vehicle (probably best to cut a bit longer than 40" so as to maximize the length of the final off-cut):
and then either draw up the physical state of one’s machine, or place the board on the machine, clamp it, and then measure its position using the machine and do the trigonometry to match the rotation and position the machine and some objects to verify the positioning — we will do the latter.
First, mark up the board using the MDF filler strip so that you will know where the cuts will be made and can clamp it in such a way that the clamps will not interfere w/ the cut:
Then jog to each corner drawn on the stock and draw in a matching circle which matches the endmill diameter (note that this will be more accurate w/ a small pointy tool, so select accordingly):