HATCHES: UNION HATCHES
APLUS can union selected hatches. APLUS will set style of first selected hatch to other selected hatches.
HATCHES: DRAW HATCH BOUNDARY
HBO command can draw boundary of selected hatch pattern. This may help you recover some lost information from a drawing.
POLYLINES: DOUBLE POLYLINE / ALIGN POLYLINE SEGMENT
With PL2 you can draw double polyline. You may specify width and justification. ALPL is a tool to align polyline segment to extension of a line or a polyline. You can fill closed polyline with termal insulation hatch with HTERM.