Mould is nature's recycler. It is a fungus. There are thousands of species. It digests organic material, both plant and animal types. The visible part is called hyphae. Hyphae grow on surfaces and internally in pourous material like wood etc. It is the internal part that make mould difficult to kill. The odour is caused by the volatile organic compounds produced by mould growth.
The VOCs are irritants. Fungal particles can make you sick in contained spaces like inside your unit. Infection in health people is rare.
Three things are necessary for mould to grow. (1) a source of organic material as food. (2) spores which are always present in the air. (3) moisture.
Mould growth is prevented by finding and eliminating the moisture source. Don't tarp your unit, it traps moisture. Allow the air to circulate so moisture can evaporate. Remove visible mould with soap and water from hard surfaces. Once mould has penetrated soft surfaces like wood you can clean the surface but you can't remove it from the interior so if moisture is present, mould growth will reappear.
Biocides must come into physical contact with the mould to prevent it from growing. Some biocides leave a residue but once the residue dissipates, mould will resume growth.
Clean your mouldered surfaces, seal as much as possible with a biocidal paint
like Kilz and above all, eliminate the moisture. Cushions, bedding etc. shouldn't be stored in your unit.