Fleece and Resin

a slead box with resin in it will only make the box more solid. For my sealed boxes I always mix a 1:1 ratio of pepto (resin and bondo) and coat the entire inside. It completely seals the box making it air tight. This results in a much tighter and cleaner sound.

IF you can push on your fleece and it flexes, then you will need to add fiberglass. If its solid as a rock dont bother.

Use both of the suggestions together and this as well...  This is a sealed speaker box.  The fleece is ONLY used for getting your structure together with all its curves and twists and blingyness.  You need to cover this fleece with fiberglass cloth and / or fiberglass mat.  I would cover the areas with at a minimum of 4 layers and then test if its going to need more.  Keep in mind, this sub box is going to contain an air volume that will be pressurized by the sub.  If you determine that no additional layers are required, then this is the time to apply your Bondo (A.K.A. - body filler) and yes, mix it with the hardener provided.  Dont use the magical "Bondo - Polyester Resin Pepto Mud Magic Mix" on it.  Save it for when more experience is evident.  As for the resin that fell/ spilled into your box....its fine, as a matter of fact, if the whole box was coated internally it would be stronger and overall will not degrade sound quality.  Also note, let the fiberglass overlap some of the wood structure as well to maintain overall adhesion.

...hope this helped....

JD