I'd try toroids on the footswitch cord first, since you say that's the worst. Then the mike and feedline.
I don't agree that an earth ground is particularly important, which is good because it's very hard to get one in most shacks and all RVs. Earth grounds are useful for avoiding electrocution, but sometimes cause electrocution too. Earth grounds aren't generally very significant for RF unless your particular antenna requires one, and even then there are workarounds.
Many airplanes have HF radios, and I've never seen an airplane with a good solid earth ground.
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-- Carl
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